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    <h1>Introduction</h1>
    <p>
      Dragonfly Room Reverb is a free stereo-to-stereo reverb effect.
      It has several different room presets, as well as a small number
      of hall presets and effect presets. It is based on ProG Reverb
      from Freeverb3VST, which uses Moorer's early reflection model
      and an implementation of Jon Dattorro's Progenitor Reverb
      algorithm.
    </p>
    <h1>User Interface</h1>
    <img src="images/dragonfly-room-reverb/interface.png" />
    <h2>Sliders</h2>
    <img src="images/dragonfly-room-reverb/sliders.png" />
    <dl>
      <dt>Dry Level</dt>
      <dd>
	<p>Level of the input signal sent directly to the reverb’s output</p>
      </dd>
      <dt>Early Level</dt>
      <dd>
	<p>Level of the early reflection signal in the reverb’s output</p>
      </dd>
      <dt>Early Send</dt>
      <dd>
	<p>Level of the early reflection signal mixed into the input to
	the late reverberation algorithm</p>
      </dd>
      <dt>Late Level</dt>
      <dd>
	<p>Level of the late reverberation signal in the reverb’s output</p>
      </dd>
    </dl>
    <p>
      The output of the Dry, Early, and Late controls are combined to
      form the reverb’s output signal. Note that sliders are not
      controlled by the presets. This allows you to set the levels in
      a way that works for your project, and then explore different
      presets without the sliders changing.
    </p>
    <h2>Basic Dials</h2>
    <p>
      Note that holding the Shift key and clicking a dial will reset
      the dial to the default for the current preset.
    </p>
    <img src="images/dragonfly-room-reverb/size-width-dials.png" />
    <dl>
      <dt>Size</dt>
      <dd>
	<p>
	  Length of the reverb’s internal delay lines. Increasing the
	  Size parameter generally leads to a smoother, less resonant
	  output however it can also increase the reverb’s attack time
	  and make individual early reflections more audible.
	  Decreasing the Size parameter generally has the opposite
	  effect, decreasing the reverb’s attack time and making
	  individual early reflections less audible although it can
	  increase the presence of metallic resonances.
	</p>
	<p>
	  In physical terms, the Size control corresponds to the
	  largest dimension of an imaginary space. When the size is
	  small, the “walls” of this space are closer together and the
	  resultant reflection density increases. When the size is
	  large, that reflection density decreases.
	</p>
      </dd>
      <dt>Width</dt>
      <dd>
	<p>
	  The Width control sets the output stereo width. Note that
	  this applies to both the early reflections and the late
	  reverberation.
	</p>
      </dd>
    </dl>
    <img src="images/dragonfly-room-reverb/predelay-decay-dials.png" />
    <dl>
      <dt>Predelay</dt>
      <dd>
	<p>
	  Delay before the onset of the late reverberation.
	</p>
	<p>
	  Note that only the late reverberation is delayed. Early
	  reflections are always output immediately. You can see this
	  by doing the following:
	  <ul>
	    <li>Set Early Level to 100% and Late Level to 0%.</li>
	    <li>Observe on the spectrogram that changing the Predelay does not move the early reflections.</li>
	    <li>Set Early Level to 0% and Late Level to 100%.</li>	    
	    <li>Observe on the spectrogram that changing the Predelay moves the late reverberation.</li>
	  </ul>
	</p>
      </dd>
      <dt>Decay</dt>
      <dd>
	Length of time for the late reverberation to decrease by 60dB.
      </dd>
    </dl>
    <h2>Preset Browser</h2>
    <img src="images/dragonfly-room-reverb/presets.png" />
    <p>
      The Preset Browser section presents the user with a range of
      room, hall, and effect presets.
    </p>
    <h2>Spectrogram</h2>
    <img src="images/dragonfly-room-reverb/spectrogram.png" />
    <p>
      The spectrogram has been included so that the user can get a
      better idea of how the various reverb parameters affect the
      plug-in’s output. The spectrogram is rendered by simulating a
      burst of white noise through the reverb algorithm with the
      current settings, and then processing the output with a fast
      fourier transform algorithm.
    </p>
    <p>
      Clicking on the “?” displays the plugin name, version, license,
      and credits.
    </p>
    <h2>Advanced Dials</h2>
    <img src="images/dragonfly-room-reverb/modulation-dials.png" />
    <dl>
      <dt>Diffuse</dt>
      <dd>
	<p>
	  Adjusts the coefficients of the allpass filters in the late
	  reverberation algorithm. It enables the user to balance echo
	  density against unpleasant colouration so that the result
	  enhances rather than detracts from the audio input signal.
	</p>
	<p>
	  A challenge that the designers of early digital reverbs
	  faced was generating a realistic number of early reflections
	  or echo density. One solution to this problem was to use
	  allpass filter networks. Although successful in increasing
	  echo density, the downside of allpass filter networks is
	  that they have a tendency to resonate, particularly when the
	  input signal is impulsive. This means that there is a
	  tradeoff between echo density and colouration.
	</p>
	<p>
	  In general, low echo density or diffusion settings increase
	  the perception of discrete echoes. In the case of
	  transient-rich sounds this can lead to “machine-gun-like”
	  effects in which individual echoes are heard. For sustained
	  sounds, this is less of an issue. Increasing the Diffusion
	  setting makes individual echoes less perceptible and
	  generally leads to a smoother, more lush reverb sound
	  however it also can introduce metallic resonances which can
	  be noticeable but depend to a large extent on the nature of
	  the input signal.
	</p>
	<p>
	  To better understand the effects of the Diffuse control,
	  open a track with clear percussive sounds. Decreasing the
	  Diffuse value will result in fewer, more discrete
	  reflections in the late reverberation. When set at very low
	  values the late reverberation has an almost "shattering"
	  sound to it. A higher Diffuse setting results in the late
	  reverberation having a smoother and richer sound.
	</p>
      </dd>
      <dt>Spin</dt>
      <dd>
	<p>
	  Rate of modulated chorus effect on the late
	  reverberation. Higher Spin values can lead to an audible
	  “wobble” particularly in real instruments such as acoustic
	  guitar or piano and can also cause noise on pure tones. This
	  effect tends to be less noticeable on speech.
	</p>
      </dd>
      <dt>Wander</dt>
      <dd>
	<p>
	  Length of modulated chorus effect on the late reverberation,
	  measured in milliseconds.
	</p>
	<p>
	  To better understand the effects of Spin and Wander, set a
	  large room size, a long delay, Modulation to 100%, and
	  Wander to 0%. Then play an abrupt sound such as a
	  percussion hit or a chord on piano or guitar. You'll notice
	  the reverb tail panning alternately left and right in the
	  stereo field at the rate set by Spin control. There are
	  multiple layers to the late reverberation, but they are all
	  synchronised in the stereo space when Wander is set to 0
	  ms. Next, increase the Wander setting, which will make the
	  layers spread out in the stereo space. The layers all still
	  spin at the same rate, but at any given time each one has
	  its own location in the stereo field.
	</p>
      </dd>
    </dl>
    <img src="images/dragonfly-room-reverb/high-dials.png" />
    <dl>
      <dt>High Cut</dt>
      <dd>
	<p>
	  Low pass filter frequency applied to the input signal before
	  it is processed by the early reflection and late
	  reverberation algorithms.
	</p>
      </dd>
      <dt>Early Damp</dt>
      <dd>
	<p>
	  Low pass filter frequency applied to the output signal of
	  the early reflection algorithm.
	</p>
      </dd>
      <dt>Late Damp</dt>
      <dd>
	<p>
	  Low pass filter frequency applied to the output signal of
	  the late reverberation algorithm.	  
	</p>
      </dd>
    </dl>
    <img src="images/dragonfly-room-reverb/low-dials.png" />
    <dl>
      <dt>Low Cut</dt>
      <dd>
	<p>
	  High pass filter frequency applied to the input signal
	  before it is processed by the early reflection and late
	  reverberation algorithms.
	</p>
      </dd>
      <dt>Low Boost</dt>
      <dd>
	<p>
	  Increases the decay time for a band of low frequencies. Note
	  that the boost feature does not have a significant effect
	  with a short decay time of less than 1s.
	</p>
      </dd>
      <dt>Boost Freq</dt>
      <dd>
	<p>
	  Approximately the top of the frequency band to be boosted.
	</p>
      </dd>
    </dl>
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